Nod mechanisms for airborne search-track antenna



TRACK ANTENNA Oct. 14, 1958 P. E. BURNS ETAL NOD MECHANISMS FOR AIRBORNE SEARCH- Filed April 8, 1957 .,s e 2% m Wm 5P. ,4 WM mgfim PW w nite f NW1) MEHANISM FUR AIRBORNE SEARCH-TRAQIK ANTENNA Paul E. Burns, Endwell, and Wayne R, Childs, Binghamton, N. Y assignors to General Electric Company, a corporation ofNew York Application April 8, 1957, Serial No. 651,235

6 Claims. (Cl. 74 -1) The present invention relates to a nodding antenna mechanism and more particularly to a nodding antenna mechanism for search and track antennas.

Generally, scanningmechanisms for locating an object and for finding and securing a specific image of such object are related to radio detection in ranging systems wherein electromagnetic waves are radiated and echoed back from distant objects. To locate an object the scanning mechanism operates in a search mode so that the reflective surface will oscillate in a predetermined pattern until the object is located. When the object is located, control of the reflective surface is changed or switched to the tracking mode so that the surface will be actuated to follow the object and thereby produce a detailed picture on the radar screen.

Some of the presently used scanning systems utilize a rack and pinion transmission arrangement to impart motion to a yoke structure pivotally associated with a reflective surface, and a system of counterweights pivoted near the center of the mechanism to attempt to dynamically balance the yoke forces when the system is operative. For example, the centrifugal force of the systems yoke structure as it progresses from the center of the rotating mechanism, where it normally is located when in a tracking mode, to a maximum offset position when in a searching mode, will not be appreciably balanced by a the centrifugal force of the counterweights operatively associated with the system in an attempt to specifically balance out the yoke forces during its movement. Hence, the centrifugal force of the yoke and the centrifugal force of the counterweights are substantially unbalanced during the antenna transition from track to search operation, and produced speed changes which are undesirable in the operation of the reflective surface.

The method utilized in the movement of the yoke and counterweights in presently used antenna scanning systems is with a rotating motor operating through slip rings driving a yoke rack through a pinion which depends on a clutch and limit switches for movement control. Consequently, the use of a rack and pinion to im part motion to the yoke, and of a system of counterweights pivoted near the center of the mechanism to attempt to dynamically balance the yoke forces does not establish a desirable criteria for the construction of efiicient and structural uncomplicated scanning systems.

The present invention comprises an antenna mechanism for providing search and track modes to a reflective surface wherein a yoke is pivotally attached to the reflective surface to give a predetermined nodding motion to the surface, and driving means continuously associated, with the yoke. Further, the mechanism is provided with motion translating means for converting linear movement to rotatory movement for predeterminedly controlling the eccentricity of the yoke relative to the driving means to control the degree of nodding in the reflectivesurface. Also, the driving means include dynamic balancing means whereby the reflective surface is balanced for all degrees of nodding. Thus, the present invention provides two Patented Get. 14, 1958 antenna mechanism will have a low power requirement in obtaining the various degrees of nodding of the reflective surface and for transition between modes, and will require nearly constant power requirements in both modes.

An object of the present invention is the provision of a nodding antenna mechanism which is dynamically balanced in its various operationalmodes and during the transition from search to track operation.

Another object is to provide an antenna mechanism having a searching operation wherein a reflective surface is sinusoidally oscillated, and a tracking operation having no oscillation.

A further object is the provision of a noddingantenna mechanism providing translation of rotation to oscillation at the reflective surface, and adjustable for various limits of oscillation.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

Figure l is a schematic view of a preferred embodiment of the invention showing the reflective surface and the driving mechanism associated therewith;

Figure 2 is a schematic view of the mechanism of Figure 1, but in greater detail to illustrate the specific coaction of the operatively associated structural members;

Figure 3 is a cross-sectional View, reduced in scale, of the embodiment taken on the line 3:43:4 of Figure 2 looking in the direction of arrows, showing the relative position of the yoke end with respect to the driving means, and the relative position of the counterweights associated therewith; and

Figure 4 is a cross-sectional view, similar to Figure 3, but indicating a change in. angular position for relative displacement between the searching mode yoke end and the driving means.

Referring now to Figure 1 of the drawings, there is illustrated a preferred embodiment 10 having two modes of antenna operation, wherein one is the sinusoidal oscillation of a reflective surface 12, such as a paraboloid, for searching operation, and a second mode without oscillation for tracking. The reflective surface 12 is pivotally mounted along a first axis to a stationary member, not shown, through pivot points 13, and pivotally mounted along a second axis, perpendicular to the first axis, to a yoke member 14 pivotally attached thereto at diametrically opposed pivot points 15. Driving means 16 are provided rotatably mounted within a housing 17 for predeterminedly oscillating the yoke member, as hereinafter disclosed.

The driving means 16, as seen in Figure 2, comprises an axially slideable shaft 18 having a cam pin 20 radially fixed therethrough for travel within a helical slot 22 formed on a sleeve member 24 which is integrally formed with a gear member 26 coaxially mounted relative to the shaft 18. A driving gear 28 is splined to the shaft 18 for rotation therewith and for relative axial movement therebetween through splinedmembers 30. A balance weight 32 is fixed to the driving gear to produce a predetermined amount of centrifugal force in all phases of operation of the preferred embodiment 10, to assist in maintaining a constant dynamic balance, as hereinafter disclosed. Rotatably journaled within the gear 28 for rotation therewith is a shaft 34 having gear means 36 at one end thereof engaging the gear 26. The other end of the shaft 34 is provided with a yoke end assembly 37, perpendicular thereto, which is formed with a balance weight 38 and an integral yoke end journalling member 40.

The shaft 34 is journaled within the gear 28 at an askew angle relative to the axis of the shaft 18, so that by rotating the shaft 34 relative to the gear 28, the position of the yoke end assembly 37 can be varied relative to the axis of the shaft 18. The end 42 of the yoke 14 is rotatably and pivotally mounted within the member 40 through suitable bearing means, such as ball bearings 44, and axially fixed relative thereto. Further, a drive gear 46, actuated by conventional power means, not shown, is provided in continuous engagement with the driving gear 28 to supply the input to the driving means 16.

The shaft 18 is axially slideable within the housing 17 through the actuation of a tilt mechanism 47 which is predeterminedly controlled to axially actuate a pair of control levers 48 which pivot intermediate levers 50 pivotally connected to a collar 52 rotatably mounted at one end of the shaft 18 and axially fixed relative thereto. The intermediate levers 50 are pivotally fixed to a number of circular springs 54 which are, in turn, fixed to a stationary member 56. The circular springs serve as a resilient fulcrum for the levers 50 when operative to and actuated by the levers 48 to axially slide the shaft 18 relative to the gears 26 and 28. Further, the springs 54 serve to bias the intermediate levers 50 to attain a predetermined amount of preloading necessary in the system to obtain positive and speedy responses.

In the operation of the preferred embodiment 10, the gears 26 and 28, and the shaft 18 splined thereto are continuously rotated at a fixed speed about the axis of the shaft. Thus, if the yoke end assembly 37 is adjusted so that the axis of the yoke end bearing 44 is not coaxial with the axis of the shaft 18, the free end 42 of the yoke 14 is rotated in a circular path. Hence, the reflector surface 12 will oscillate about the axis of the pivot points 13, and thereby operate in the search mode. If the free end 42 of the yoke is returned to a position perpendicular to the point of intersection of the axes of the pivot points 13 and 15, the reflective surface will not oscillate and therefore operate in the tracking mode. In this tracking mode, as seen in Figure 2, the axis of the yoke 14 will be coaxial with the axis of the shaft 18.

Thus, the degree of oscillation or nodding of the reflective surface 12 about the axis of the pivot points 13 is determined by the suitable actuation of the tilt mechanism which in turn, imparts linear motion to the control levers 48 which pivot levers 50 about the circuit springs 54. Pivoting of the levers t) imparts a linear motion to the collar 52 which is transmitted to the shaft 18. Axial movement of the shaft 18 linearly displaces the radial pins 20 which, in turn, travels within the helical slot 22 to convert linear motion of the shaft 18 into rotary motion of the sleeve 24.

Rotation of the sleeve 24 will rotate the gear 26 relative to the shaft 18 and rotate the gear 36 at one end of the shaft 34. In this manner, the yoke 14 with its end 42 rotatably journaled within the bearing 44, will be predeterminedly displaced relative to the axis of the shaft 18 to determine the amount of nodding in the reflective sur face 12 about the pivot axis 13. Reversal of the tilt mechanism will, of course, change the mode and, as shown in Figure 2, the yoke end assembly 37 can be angularly adjustable through a substantially large angle, such as 180.

In Figure 3 the yoke end assembly 37 is shown in the tracking mode wherein the axis of the shaft 18 is coaxial with the shaft of the yoke end 42 and, of course, with the axis of the bearing 44.- Figure 4, illustrates a displacement of of the weight 38 so that the embodiment 10 is now in the searching mode. It can be seen from Figure 4, that with the yoke end 42 at W3, the centrifugal force of W3 plus W4, will equal the centrifugal force acting at W2 and will, in turn, equal the centrifugal force of W1 about the axis of the shaft 18. As W3 and W4 rotate about the axis of the shaft 34 to change modes, one centrifugal force decreases at the same rate the other increases, so that the total centrifugal force through W2, about the rotational axis of the yoke end assembly 37, always remains constant and equal to the centrifugal force of W1, the weight integral with the driving gear 28. Thus, the operative coaction of the counterweights maintains the embodiment 10 dynamically balanced at all times.

In brief, the present invention discloses a nodding or oscillating antenna mechanism which can proceed from a search mode to a tracking mode, or vice versa, without stopping, while being dynamically balanced at all times, and which translates linear control to rotational motion and, in turn, to oscillation of the reflective surface without excessive mechanical vibration and without excessive bearing wear to obtain a smooth operating system.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. An antenna mechanism adapted for search and track modes of operation comprising a reflective surface pivotally mounted on two axes perpendicular to each other, a yoke pivotally attached to said surface along one of said axes, a yoke end assembly operatively coupled to said yoke, driving means rotatably coupled to said yoke end assembly for mutual rotation, yoke adjusting means rotatably coupled to said driving means and to said yoke end assembly for mutual rotation therebetween,

linear actuated means rotatably coupled to said yoke adjusting means for controlling the relative angular position of said yoke end assembly relative to said driving means by controlling the eccentricity of the axis of the yoke relative to the axis of rotation of said driving means, and control means coupled to said linear actuated means for determining the extent of linear actuation.

2. A nodding antenna mechanism comprising a reflective surface having two pivot axes perpendicular to each other, a yoke member pivotally attached to said surface for nodding said surface about one of said pivot axes, driving means operatively associated with an adjustable member connected to said yoke and rotatably coupled to said driving means for nodding said reflector, a driving gear operatively coupled to said driving means for continuously rotating said adjustable member about a predeterminedly adjustable axis, integral with said driving means and said adjustable means including balancing means for balancing the mechanism at all times.

3. A nodding mechanism for search and track antennas comprising a reflective surface having a plurality of pivoting axes, yoke means secured to said surface about one of said pivoting axes, driving means operatively coupled to said yoke for rotating the end of said yoke in a circular path, adjusting means operatively associated with said driving means to translate linear motion to rotating ,motion for varying the position of the end of said yoke relative to the axis of rotation of said driving means.

4. A scanning mechanism comprising a reflective surface, a yoke pivotally attached to said surface to impart a predetermined nodding motion thereto, driving means continuously associated with said yoke and juxtaposed to the end thereof, a motion translating means rotatably associated with said driving means for converting linear motion to rotating motion to predeterminedly control the eccentricity of the end of said yoke relative to the axis of said driving means for controlling the degree of nodding in said surface, and counterweight balancing means operatively associated with said driving means and with the end of said yoke for balancing said reflective surface in all operative degrees of nodding.

5. A nodding antenna comprising a reflective surface having a number of pivot axes, first means coupled to said surface to oscillate it about one of said axes and transfer means operatively connected to said first means for translating linear motion to rotary motion for controlling the degree of oscillation of said reflective surface, and driving means rotatably coupled to said first means and transfer means to continuously rotate both means.

6. An antenna mechanism for search and track antennas comprising reflective means pivotally mounted on two pivot axes perpendicular to each other, yoke means pivotally coupled to said reflective surface along one of said pivot axes, driving means operatively coupled to said yoke, adjusting means operatively coactitng With said driving means and said yoke means for controlling the eccentricity of the axis of said yoke relative to the axis of said driving means, linear responsive means coupled to said adjusting means for relative rotation therebetween, spring biased lever means coupled to said linear responsive means for controlling the relative axial displacement relative to said driving means and for determining the degree of relative rotation between said linear'responsive means and said adjusting means.

References Cited in the file of this patent UNITED STATES PATENTS 2,699,502 Hohl et al. Jan. 11, 1955 

